As shown in FIG. 1, a conventional 8031 micro-controller system generally comprises an 8031 micro-controller 1, an address latch 2, a flash memory 3, and a static random access memory (SRAM) 4.
The multiplex bus (AD0˜AD7) and the address latch enable (ALE) pin of the 8031 micro-controller 1 are respectively connected to the address latch 2 for storing address signals in the registers so as to facilitate the execution of reading and writing actions of the 8031 micro-controller 1. The output of the address latch 2 is connected to both the flash memory 3 and the SRAM 4. The outputs of the flash memory 3 and the SRAM 4 are connected to the multiplex bus (AD0˜AD7). The address bus (A8˜A15) of the 8031 micro-controller 1 is connected to both the flash memory 3 and the SRAM 4. The write enable (WE) pin and the output enable (OE) pin of the SRAM 4 are respectively connected to the read (RD) pin and the write (WR) pin of the 8031 micro-controller 1. The write enable (WE) pin and the output enable (OE) pin of the flash memory 3 are respectively connected to 5V and the program store enable (PSEN) pin of the 8031 micro-controller 1.
Due to property of the flash memory 3, the flash memory 3 is used as a read only memory (ROM) for storing machine codes of the 8031 micro-controller 1. It means that the flash memory 3 generally only can be read out but can't be written in when the 8031 micro-controller 1 fetches and executes machine codes. The SRAM 4 is the only place that the 8031 micro-controller 1 can write and retrieve data. Thus, the 8031 micro-controller 1 successively executes machine codes fetching from the flash memory 3, and stores the operation results to the SRAM. If it is necessary to renew the content of the flash memory 3, the only way is to replace the original flash memory with a new flash memory. Therefore, the cost will be relatively high.